Reading the FAQ of the database, it appears that in order for a product to be deemed compatible, Microsoft considers several aspects such as the product passing the Windows certification requirements and receiving a logo, something which appears to apply to Red Dead Redemption in this case.

Furthermore, reading the partner’s submission page, it mentions that the app can only appear on the list either by a developer submission or by Microsoft testing, and that qualifying submissions will be published in the Windows Compatibility Center,” all of which apply to the game here.